A virtual machine (VM) comprises virtualized representations of real hardware, software, and firmware components available in a data processing system. The data processing system can have any number of VMs configured thereon, and utilizing any number of virtualized components therein. The data processing system is also referred to as a computing node, a compute node, a node, or a host.
For example, the host may include a processor component. One virtual representation of one portion of the capacity of the processor can be assigned to one VM, and another virtual representation of another portion of the capacity of the same processor can be assigned to another VM, both VMs executing on the host. Furthermore, the second VM may also have access to a virtual representation of a reserve processor in the host and certain other resources, either exclusively or in a similar shared manner with the first VM.
Certain data processing systems are configured to process several workloads simultaneously. For example, separate virtual data processing systems, such as separate VMs, configured on a single host data processing system often process separate workloads for different clients or applications. In large scale data processing environments, such as in a data center, thousands of VMs can be operating on a host at any given time, and hundreds if not thousands of such hosts may be operational in the data center at the time.
VMs are installed or created on a compute node as needed for processing workloads, meeting service level requirements, and many other reasons. Furthermore, different configurations of VMs may be needed for different purposes. For example, when a VM is created just for providing a user a general purpose computing platform, the VM may be created only with the basic operating system and no applications. In another example, when a new VM has to provide application services, the VM may be created with an operating system and an application server configured thereon. Similarly, many different configurations of VMs may be created for a variety of other purposes.
An image is a binary package that can be installed to instantiate a VM on the hardware. A layer is a software package that participates in an image. An image can include any number of software packages, whose layers are assembled together in the image as a monolithic binary. A single image can, but need not necessarily, represent an application.
A commonly used method of virtualization—traditional virtualization—preconfigures various VM configurations as template images (templates). When a VM having a specific predetermined configuration has to be created on a compute node, a suitable template is selected from a template storage, such as a database or a file-system, and installed on the compute node to create a VM having the desired configuration. An image of a VM in traditional virtualization is a monolithic binary image.
Another method for virtualization is container-based virtualization. Container-based virtualization, also called operating system virtualization, is an approach to virtualization in which the virtualization layer runs as an application within the operating system. In this approach, the operating system's kernel runs on the hardware node with several isolated guest VMs installed. The isolated guests are called containers.
With container-based virtualization, there isn't the overhead associated with having each guest run a completely installed operating system. This approach can also improve performance because there is just one operating system taking care of hardware calls. A disadvantage of container-based virtualization, however, is that each guest must use the same operating system the host uses.
Container-based virtualization is a way to operate several containers on the same host, where the containers share the same kernel and memory space among themselves and with the virtual machine and host. The isolation between the containers occurs at multiple resources, such as at the file-system, the network stack subsystem, and one or more namespaces, but not limited thereto. By sharing the same running kernel and memory space there is virtually no difference between the performance of the “host” operating system and the containers.
This method of virtualization is significantly different from the traditional virtualization technology where the hardware is emulated using a software emulation layer, which causes provisioning latencies, slow startup times, and decreased performance of the underlying hardware. These and other drawbacks of the traditional virtualization method are due to the software emulation layer that sits between the physical hardware of the host and the operating system that is being run on top of the emulated hardware.
The container-based virtualization technology offers higher performance and less resource footprint when compared to traditional virtualization, and has become an attractive way for cloud vendors to achieve higher density in the datacenter. Thus, containerization (i.e., operating a virtualized data processing environment using container-based virtualization) is changing how workloads are being provisioned on cloud infrastructure.
Hereinafter, a reference to a virtualized computing entity (VCE) is a reference to a VM or a container, depending upon the environment in which an embodiment is implemented. An embodiment described herein with respect to a VM can be adapted by those of ordinary skill in the art to operate in a containerized environment, and vice-versa, and such adaptations are contemplated within the scope of the illustrative embodiments.